1. Field of the Invention
The present invention relates to a control valve for a variable displacement compressor used for a car air-conditioner and the like, and more particularly, to a control valve for a variable displacement compressor capable of hardly causing operation failure of a valve rod.
2. Description of the Conventional Art
Generally in a conventional control valve for a variable displacement compressor used for a car air-conditioner and the like, refrigerant having discharge pressure Pd is introduced from a compressor (a discharge chamber of a compressor) and is throttled so as to be introduced to a crank chamber, in order to adjust a pressure Pc in the crank chamber of the compressor. An introducing amount (a throttling amount) into the crank chamber is controlled corresponding to a suction pressure Ps of the compressor. As for the basic constitution of the control valve, as described in Japanese Patent Application Laid Open No. 2003-172256 for example, the control valve for a variable displacement compressor includes a valve rod having a valve body part; a valve main body which has a guiding hole in which the valve rod is slidably inserted, a valve chamber having a valve port to/from which the valve body part contacts/separates, a discharge pressure refrigerant inlet provided at an upstream side than the valve port for introducing refrigerant having discharge pressure from the compressor and a refrigerant outlet provided at the downstream side than the valve port so as to communicate with a crank chamber of the compressor; an electromagnetic actuator having a coil, a cylindrical stator arranged at the inner periphery side of the coil, an attraction piece fixed to the stator, a plunger arranged at the lower side than the attraction piece so as to be upwardly and downwardly slidable, a plunger spring arranged between the attraction piece and the plunger, and a guiding pipe in which the plunger is slidably inserted; a pressure sensing chamber formed at the upper side than the attraction piece, into which a suction pressure is introduced from the compressor; a pressure sensitive response member for pressing the valve rod in the valve opening direction corresponding to a pressure of the pressure sensing chamber; and a valve closing spring for energizing the valve rod in a valve closing direction.
In the conventional control valve having such the constitution, when the electric current is applied to the coil of the electromagnetic actuator, the plunger is attracted to the attraction piece. Then, the valve rod is moved in the valve closing direction following the plunger by energizing force of the valve closing spring. On the other hand, refrigerant having a suction pressure Ps introduced from a compressor to a suction pressure introducing inlet is introduced into the pressure sensing chamber from an introduction chamber through a clearance formed between the plunger and a guiding pipe arranged on the outer periphery of the plunger. The pressure sensitive response member (for example, a bellows device) is displaced so as to extend or contract corresponding to the pressure (the suction pressure Ps) in the pressure sensing chamber (the member contracts when the suction pressure Ps is high, and extends when the suction pressure Ps is low). The displacement (pressing force) is transmitted to the valve rod, so as to control a valve opening. The valve opening is determined by the attracting force of the attraction piece to the plunger, the pressing force of the pressure sensitive response member, and the energizing forces of a plunger spring (a valve opening spring) and a valve closing spring. Corresponding to the valve opening, the introducing amount (the throttling amount) into the outlet side, that is, into the crank chamber, of the refrigerant having a discharge pressure introduced into the valve chamber from the discharge pressure refrigerant inlet, is adjusted, so as to control the pressure Pc in the crank chamber.
However, the above-described control valve has the constitution in which the valve rod moves in the valve closing direction by only the energizing force of the valve closing spring. So, the operation failure of locking of the valve rod or the like is caused when a foreign matter is clogged between sliding faces of the valve rod and the guiding hole or the sliding resistance of the valve rod is increased by oil seizing or the like. For example, there is a problem that even when the plunger is attracted by the attraction piece, the valve rod does not move in the valve closing direction so as to be inactive. In such case, the valve opening is not properly controlled. In order to solve such the operation failure, the energizing force of the valve closing spring may be increased. However, if the energizing force is increased, the energizing force of the plunger spring (the valve opening spring) must be also increased. As a result of this, the sizes of springs and a product are increased, so that the cost is increased.
So, in order to solve the problems, Japanese Patent Application Laid Open No. 2004-100473 proposes a control valve, in which a plunger and a valve rod are directly connected (integrated), so as to forcedly move the valve rod in the valve closing direction together with the plunger when the plunger is attracted by a attraction piece.
However, the above-described control valve in which the plunger and the valve rod are directly connected has the following problems.
When electric current is applied, the plunger may move upwardly and downwardly (in the valve opening and closing directions) while being laterally deviated (moved to one side) or inclined depending on a magnetic circuit (due to the concentricity of the attraction piece and the plunger). Thereby, if the plunger and the valve rod are connected without a backlash, the valve rod is pushed to the guiding hole according to the deviation or inclination of the plunger so as to increase sliding resistance. As a result, the valve rod and the plunger do not smoothly move, so as to cause operation failure such as locking, which is similar to the above-described problem.
Further, when the plunger and the valve rod are directly connected, the size management and assembling accuracy of parts are hardly achieved due to the above-described problem, and the cost may be increased.